1. Field of the Invention
The present invention relates to components for medical circuits for conveying gases to and/or from a patient. In one particular aspect, the invention relates to conduits and in particular to heated breathing tubes for use in an inspiratory and/or expiratory limb of a breathing circuit. In another particular aspect the invention relates to a heated tube for a surgical insufflation system.
2. Description of the Related Art
In assisted breathing, particularly in medical applications, gases having high levels of relative humidity are supplied and returned through flexible breathing tubes of a relatively restricted size typically between a range of approximately 10 mm to 25 mm diameter (covering both neonatal and adult applications). Such breathing tubes are ideally very light, resistant to kinking or pinching but also very flexible to ensure the greatest performance and level of comfort for the patient. The light weight of a breathing tube is very important to reduce any forces applied to the patient interface by the weight of the tube. Similarly, breathing tubes must be flexible and able to bend easily to achieve a high level of patient comfort, which in turn can improve patient compliance.
In medical applications, such as with assisted breathing, the gases inhaled by a patient are preferably delivered in a condition having humidity near saturation level and at close to body temperature (usually at a temperature between 33° C. and 37° C.). Condensation or rain-out can form on the inside surfaces of the breathing tubes as the high humidity breathing gases cool and/or come into contact with the relatively cooler breathing tube surface. Breathing gases exhaled by a patient are usually returned fully saturated and flow through an expiratory breathing tube. If the expired gas is allowed to cool as it passes along an expiratory breathing tube, condensation or rain-out may also occur.
Similarly, Continuous Positive Airway Pressure (CPAP) systems or positive pressure ventilation systems that provide patients suffering from obstructive sleep apnoea (OSA) with positive pressure breathing gases, also use breathing tubes for delivering (or removing) inspiratory (and/or expiratory) gases.
Condensate forming in a breathing tube (either inspiratory or expiratory) can be breathed or inhaled by a patient and may lead to coughing fits or other discomfort. Condensation within a breathing tube may also interfere with the performance of connected equipment and ancillary devices and/or various sensors.
Attempts have been made to reduce the adverse effects of condensation by either reducing the level of condensation, or providing collection points for draining condensed liquid from the tubing component. Reducing the condensation or rain-out has generally been achieved by maintaining or elevating the temperature above the dew point temperature of the breathing gas to reduce the formation of condensation. This temperature is typically maintained by a heater wire within the breathing tube, although the rain-out performance of these breathing tubes may not be complete due to a number of factors. Further, previous methods of heating the gases flow to reduce rain-out, typically result in heated tubing that has been expensive and/or difficult to manufacture. Particularly, in ‘single use’ applications such as typically found in hospital applications, the manufacturing cost of breathing tubes is critically important. It is highly desirable to even further reduce rainout, while preferably maintaining a low production cost, for example, by utilising a manufacturing method that is capable of high production speeds.
Similarly, during laparoscopic surgery with insufflation, it may also be desirable for the insufflation gas (commonly CO2) to be humidified before being passed into the abdominal cavity. This can help prevent ‘drying out’ of the patient's internal organs, and can decrease the amount of time needed for recovery from surgery. Even when dry insufflation gas is employed, the gas can become saturated as it picks up moisture from the patient's body cavity. The moisture in the gases tends to condense out onto the walls of the medical tubing or discharge limb of the insufflation system. The water vapour can also condense on other components of the insufflation system such as filters. Any vapour condensing on the filter and run-off along the limbs (inlet or exhaust) from moisture is highly undesirable. For example water which has condensed on the walls, can saturate the filter and cause it to become blocked. This potentially causes an increase in back pressure and hinders the ability of the system to clear smoke. Further, liquid water in the limbs can run into other connected equipment which is undesirable.
In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.